摘要:

The use of bias light is common practice today in photoconductance decay (PCD) measurements to analyze semiconductor samples with injection‐level dependent recombination parameters (i.e., surface recombination velocity and/or bulk lifetime). Recently, it has been shown on theoretical grounds that the previously reported recombination parameters from light‐biased PCD experiments are not theactualproperties of the investigated sample, but so‐calleddifferentialrecombination parameters [R. Brendel, Appl. Phys. A60, 523 (1995)]. In the present article the theory relevant to light‐biased PCD measurements is discussed in detail and subsequently applied to monocrystalline silicon wafers with nitride and oxide passivated surfaces in order to verify the deviations between the differential and actual surface recombination velocities. Special emphasis is paid to the experimental fact that the injection level cannot be reduced below a minimum value due to signal‐to‐noise problems. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360990

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The sensitivity of a contactless measurement procedure to determine the minority‐carrier recombination parameters in Si wafers is analyzed. The measurement is based on the harmonic generation of excess carriers, whose time dependence is measured either by &mgr;‐wave reflection or free‐carrier absorption. Both the measurement equipment and the model used to extract the surface recombination velocity and the bulk carrier lifetime are introduced and the sensitivity of the parameter fit procedure is examined. The results of this uncertainty analysis are applied to typical experimental situations, e.g., bulk minority carrier lifetime measurement of a monocrystalline wafer with equal surfaces or a bulk minority carrier lifetime mapping done on an as‐grown multicrystalline Si wafer before it obtained saw damage removal. The method proves to be very useful, if the interpretation of the results is carefully done and an appropriate experiment is chosen to produce the best possible results. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360991

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a study of the generation of slow interface states (time constants ≳40 s) by vacuum ultraviolet irradiation (Kr lamp,h&ngr;=10 eV) on metal–oxide–silicon samples with approximately 30 nm of thermally grown SiO2and a transparent aluminum gate. The density of the centers in a given energy range was obtained from the shift of the midgap voltage over this range. A detailed energy level spectrum was determined from the stabilization times of the charging or discharging current observed after each of a series of 0.1 V steps in the bias voltage. Peaks in the energy level spectrum were observed for a position of the Fermi level at the Si–SiO2interface near the band edges, at ≊0.25 eV above the valence‐band edge and at ≊0.65 eV above the valence‐band edge. The corresponding defects are identified as the oxygen vacancy, thePbcenter (tentatively), and a hydrogen atom trapped at an oxygen atom in a strained Si–O–Si configuration near the Si/SiO2interface. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360992

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have calculated tunneling conductance in metal–narrow‐gap‐semiconductor (NGS)–metal tunnel junctions. Flietner’s two‐band model is used to describe the dispersion relation within the energy gap in an isotropic NGS with different conduction‐ and valence‐band edge effective masses. The results are compared with the tunneling conductance calculated by Kane’s two‐band model, which has been commonly used to describe the tunneling characteristics through the energy gap in semiconductors. These results propose that the tunneling conductance in the tunnel junctions in which a narrow gap semiconductor of largely different conduction‐ and valence‐band effective masses is used as a tunneling barrier can exhibit quite a different behavior, especially in the region of the midgap, from the tunneling conductance described by Kane’s two‐band model. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360993

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electronic sources based upon resonant tunneling diodes (RTDs) usually generate power by establishing limit cycles which exchange energy with storage elements in an external biasing circuit; hence, the output power in this type of implementation will always be limited by extrinsic effects. We verify the presence of multiple energy‐storage mechanisms solely within the RTD and characterizes the interdependencies necessary to induce intrinsic oscillations observed in quantum mechanical simulations. Specifically, we show that a nonlinear ‘‘access’’ resistance and quantum‐well inductance is responsible for the hysteresis, ‘‘plateaulike’’ behavior, and bistability associated with the intrinsic current–voltage (I–V) characteristic. Furthermore, a new circuit‐level representation which accurately incorporates the nonlinear dependencies into these heretofore ‘‘linear’’ equivalent‐circuit elements is used to demonstrate the different roles, as well as the degree of cooperative interplay, of the intrinsic oscillations and hysteresis in determining the overallI–Vcharacteristics of the RTD.

ISSN:0021-8979    

DOI:10.1063/1.360994

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a detailed investigation of electron tunneling in (Ga,In)As/(Al,In)As asymmetric double quantum wells as a function of different excitation and temperature conditions. We show that tunneling dynamics depend strongly on the initial carrier temperature and momentum. For example, electron and hole tunneling out of the narrow well is complete at low temperature. However at room temperature carriers do not exhibit any tunneling kinetics. We propose a simple kinetic model which describes the observed population dynamics at different carrier densities, temperatures, and excitation conditions. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360995

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ballistic electron emission microscopy (BEEM) has been performed on Au/ZnSe (001) diodes prepared in ultra high vacuum. An average barrier height (BH) of 1.37 eV is found for Au/n‐ZnSe in close agreement with previously published values for diodes measured by conventional techniques. The BH distribution is relatively narrow, from 1.32 to 1.43 eV, consistent with cross‐sectional transmission electron microscopy which indicates that the interface is abrupt, and without reaction products. These results differ from those reported for BEEM measurements on chemically etched Au/ZnSe diodes. [R. Coratgeretal., Phys. Rev. B.51, 2357 (1995)]. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360996

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper presents a theoretical analysis of the scattering potentials associated with dislocations in the case of two dimensional electron gas. It is shown that dislocations act mainly on the free carrier mobility through the potential associated with their linear electric charge and not with their strain field potentials. Two different experimental cases, both supported by GaAlAs‐GaInAs‐GaAs samples, have been considered: (i) samples containing long misfit dislocations issuing from a partial relaxation, during the crystal epitaxial growth and (ii) samples containing dislocation segments introduced by plastic deformation. It is shown that in the case of long misfit dislocations, the free carrier mobility parallel to the dislocations remains unaffected by dislocations while it is probably controlled by some tunneling effect in the direction perpendicular to the lines. In the case of dislocation segments, the free carrier mobility is controlled in both directions by a diffusion process which may be described with the help of a phenomenological potential. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360997

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article deals with the influence of dislocations on the conductivity of two dimensional electron gas measured at helium temperature and at high magnetic field. Two kinds of dislocation substructures have been experimentally studied: they correspond either to a family of parallel dislocation segments introduced by plastic bending or to a family of parallel and long misfit dislocations created during the epitaxial growth by the control of the epilayer thickness. It is shown that both types of dislocation substructure lead to a strong anisotropic behavior of the longitudinal conductivity while the quantum Hall effect is not significantly affected by the presence of dislocations. A theoretical treatment of the case of anisotropic potentials is proposed as a generalization of the simpler case, addressed in the literature, of isotropic (short range) potentials. With the help of this analysis, we can explain, in the case of the dislocation segments, why although anisotropic, the normalized conductivity curves obtained in the principal axis are identical and we show that regular Dingle plots may be used to check the extra broadening of the Landau levels due to dislocations. The second kind of dislocation substructure is shown to be equivalent to quasi one dimensional systems issuing from a truncation of the two dimensional electron gas into quite parallel ribbons localized between the dislocation potential barriers, but no ballistic effects could be observed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360998

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Films of poly‐(2‐phenyl‐1,4‐phenylene‐vinylene) (PPPV) and photodiodes with PPPV as an active layer were studied by optically (ODMR) and electrically (EDMR) detected electron‐spin resonance (ESR). Two different signals were observed in ODMR: enhancement of the photoluminescence (PL) atg=2.01 due to recombination of the photogenerated polarons (s=1/2), and a half‐field enhancement signal, attributed to the fusion of triplet excitons. Both processes lead to the formation of singlet excitons. The spectral dependence of thes=1/2 signal follows the low energy part of the PL spectrum, indicating that delayed recombination of distant polarons is influenced by ESR, whereas the cw PL contains both prompt and delayed contributions. The linewidth and the intensity of the ODMR signal depend on the PL excitation intensity. Both effects are due to a decrease of the recombination lifetime of the polaron pairs at higher intensities. The relative decrease of the short‐circuit photocurrentISCthrough a PPPV photodiode by ESR saturation is due to recombination of nonthermalized, nongeminate excess charge polarons in the active layer of the device. This effect is at least two orders of magnitude stronger than the enhancement of total PL at the same temperature. This feature is found to be common for conjugated polymers investigated so far, and reflects the fact that the total photogeneratedISCis spin dependent, whereas ODMR selects only the nongeminate portion of recombining species in the sample. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360999

出版商:AIP    

年代:1996

数据来源: AIP